[Python-Dev] Making sure dictionary adds/deletes during iteration always raise exception

[INADA Naoki]

When adding new key, dk_usable is decremented.
When removing key, dk_usable is not decremented.

So I think dk_usable & ma_used pair can be used to detect dict size
modification.

On Wed, Dec 14, 2016 at 8:02 AM, Serhiy Storchaka <storchaka at gmail.com> wrote:
> On 13.12.16 11:51, Max Moroz wrote:
>>
>> Would it be worth ensuring that an exception is ALWAYS raised if a key
>> is added to or deleted from a dictionary during iteration?
>>
>> Currently, dict.__iter__ only raises "RuntimeError" when "dictionary
>> changed size during iteration". I managed to add 1 key and delete 1
>> key from the dictionary in the same iteration of the loop (the code
>> was in a callback function invoked in the loop) - of course without
>> any exception. (I hope I'm right in assuming that adding and deleting
>> entries in the loop is unsafe whether or not number of adds equals
>> number of deletes.)
>>
>> I suspect the cost of a more comprehensive error reporting is not
>> worth the benefit, but I thought I'd ask anyway.
>
>
> The patch implementing this was rejected.
>
> http://bugs.python.org/issue19332
>
>
>
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-- 
INADA Naoki  <songofacandy at gmail.com>